需求
项目中需要在一个utils工具类中，调用mapper对象进行查询并进行排序后选出数值最小的数值，然而静态方法里面直接注入会报空指针的错误。现在总结一下解决办法。
重要点
1、若要进行排序，需要重写该实体类的compareTo()方法,实现Comparable接口。代码如下
@Override public int compareTo(Object o) { if(o instanceof TbHotelMenu){ TbHotelMenu menu=(TbHotelMenu) o; int oP = (int) Double.parseDouble(menu.getMenuPrice()); int tP = (int) Double.parseDouble(this.getMenuPrice()); return tP-oP;//升序 //return tP-oP;//降序 } return 0; }
2、需要将该工具类注入到spring 。applicationContext-service.xml配置文件代码如下
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.0.xsd "> <!-- 扫描包加载Service实现类 --> <context:component-scan base-package="com.test.server.service"></context:component-scan> <context:component-scan base-package="com.test.server.util"></context:component-scan>
3、
a、utils类上面添加@Component注解
b、@Autowired注入需要使用的mapper对象，注意不是静态的
c、创建一个静态的这个utils的对象
d、创建一个init方法，添加@PostConstruct注解，代码内容如下
@Component public class LowestMenuPrice { @Autowired private TbHotelMenuMapper menuMapper; private static LowestMenuPrice menuPrince; @PostConstruct public void init(){ menuPrince = this; menuPrince.menuMapper = this.menuMapper; } //获取酒楼菜单价钱最低的菜单价格 public static String getLowestPrince(long hotelId){ TbHotelMenuExample example=new TbHotelMenuExample(); TbHotelMenuExample.Criteria criteria = example.createCriteria(); criteria.andHotelIdEqualTo(hotelId); List<TbHotelMenu> menuList = menuPrince.menuMapper.selectByExample(example); if(menuList!=null&&menuList.size()>0){ Collections.sort(menuList); String menuPrice = menuList.get(0).getMenuPrice(); Double valueOf = Double.valueOf(menuPrice); DecimalFormat Format=new DecimalFormat("#.00"); String price=Format.format(valueOf); return price; } return "0.00"; } }
